This invention relates to a magnetron, and more particularly to the improvement of outer members force fitted onto the main body of the magnetron.
Magnetrons are widely used for defreezing and heating foodstuffs since they can generate efficiently microwaves when incorporated into microwave ovens. In most prior art magnetrons, parmanent magnets are arranged on the outside of the evacuated envelope but in recent years, research has been made to install the magnets within the envelope for the purpose of miniaturizing the magnetron and improving the productivity and reliability.
FIG. 1 is a longitudinal sectional view showing the basic construction of one example of a prior art magnetron comprising an evacuated envelope, a cylindrical anode electrode 1a contained in the envelope and provided with a plurality of radial vanes 1i, permanent magnets 1b and 1c supported by supporters 1e and 1f at the upper and lower ends of the anode electrode, a cathode electrode 1d concentrically contained in the anode electrode, a cathode lead 1g for supplying heating current to the cathode electrode, an output electrode 1h or antenna for radiating the microwave created in the resonator comprised of vanes of the anode electrode.
On the outer periphery of the envelope is secured a mounting plate 2 for mounting the magnetron on a microwave oven, not shown, heat radiating fins 3 for dissipating the heat generated by the anode electrode 1a, and a filter casing 4 for shielding the cathode lead 1g through their annular portions 2a, 3a and 4a respectively as by force fitting or shrink fitting. Waveguide members 6a and 6b are secured to the mounting plate 2 with a gasket 5 interposed therebetween by means of screws 7 so as to cover the antenna 1h. In other words, the magnetron is suspended from the waveguide through the annular portion 2a of the mounting plate 2.
With the construction described above, however, problems arise when the inner diameter of the annular portion or the outer diameter of the envelope is not accurate. Particularly, since the main body 1 of the magnetron is supported only by the mounting plate 2 with its annular portion 2a force fitted on the outer periphery of the envelope, the envelope would be withdrawn from the mounting plate if an excessive force is applied to the envelope in the axial downward direction thereof when the waveguide member 6b presses down the envelope through the gasket 5 as the screws 7 are tightened. As the cooling fins 3 are formed by pressing metal sheets (usually aluminum sheets), their upright flanges 3a often become irregular and eccentric thus forming air gaps between the flanges and the envelope which decreases heat dissipation. Further such flanges are deformed due to heat generated during the operation.